The present invention relates to playgrounds and other recreational areas, and more particularly to layered base and sub-base constructions supporting recreational surfaces.
Years ago, most playgrounds and other recreational areas had natural grass surfaces. Natural grass, although suitable for play surfaces, requires ongoing maintenance, e.g., mowing and weed control. The underlying soil is subject to erosion, and may exhibit poor drainage. In certain heavily used areas of the play surface, the soil tends to become compacted. This prevents the growth of grass, giving the play surface an undesirable appearance. Also, the compacted soil as compared to undamaged turf has a reduced capacity to absorb shock, and thus presents an increased risk of injury due to falls.
Given the above disadvantages, designers of recreational areas have turned to alternatives, including a variety of loose-fill materials such as sand, gravel, wood mulch, wood chips and rubber particles or fragments.
Rubber particles are receiving more attention now, largely due to concerns about playground safety, particularly with respect to reducing injury due to impact from a fall onto the play surface. The U.S. Consumer Product Safety Commission, in a study of equipment-related injuries on playgrounds, has concluded that the majority of such injuries occur due to falls from the equipment to the ground surface below the equipment. The Commission has tested a variety of loose-fill materials used in constructing playgrounds and recreational sites, determining, with respect to a particular material, a "critical height" for a given thickness of a layer of the material. The critical height is the maximum height from which an instrumented metal head form, upon impact, yields (1) a peak deceleration of no more than 200 g's, and (2) a head injury criterion (HIC) of no more than 1,000. The HIC measurement takes into account the duration of an acceleration as well as the acceleration itself. In any event, the critical height is intended to approximate the maximum height of a fall from which a life-threatening head injury is not expected.
The loose-fill materials for which critical height information is available include wood mulch, double shredded bark mulch, uniform wood chips, fine sand, coarse sand, fine gravel, and medium gravel with particles up to about 1/2 inch in diameter. At a material depth of 6 inches, wood mulch exhibits the best critical height, i.e. 7 feet. At a depth of 12 inches, uniform wood chips provide the only uniform height above 12 feet. Wood mulch and double shredded bark mulch exhibit critical heights of 11 feet at the 12-inch depth. By comparison, coarse sand and medium gravel at that depth have critical heights of 6 feet.
Particles of rubber or other elastomers are expected to exhibit critical heights superior to the critical heights of the tested materials, given their superior resilient and shock absorbing qualities. However, ultraviolet rays deteriorate the appearance of rubber particles. Also, there are several safety concerns, including a potential fire hazard, and the possible attractiveness of rubber particles to small children, who may consume the particles or choke on larger particles.
All loose-fill materials require a border or wall for containing the material. Walls can be formed by excavation or by above-ground components, e.g. landscaping ties or blocks of concrete or stone. To avoid the need for containment, a variety of synthetic products have been developed. These include continuous matting, or combinations of base sheets with upright synthetic fibers or pile to simulate grass. Some of the synthetic layers incorporate ribs to form compartments for either ambient or compressed air, as in U.S. Pat. No. 4,991,834 (Vaux), and U.S. Pat. No. 5,254,039 (Garcia).
Other turf designs have incorporated loose-fill materials. For example, U.S. Pat. No. 4,396,653 (Tomarin) discloses a synthetic pile carpet including a base sheet and synthetic fibers extending vertically from the base sheet to simulate grass. A layer of rubber particles, i.e. "crumb rubber" is applied over the base sheet, with a coarser, sand-like layer applied over the rubber particles. Both particulate layers thus intermingle with the upright synthetic fibers. In U.S. Pat. No. 4,044,179 (Haas), a recreational area construction includes a subsurface, a pile fabric including a backing and upstanding elements to simulate grass, and granular material distributed among the upstanding elements. A primary concern with synthetic turf or matting is the prohibitive expense.
In connection with rubber particles as a loose-fill, U.S. Pat. No. 5,014,462 (Malmgren) discloses the use of solid rubber particles mixed into soil, primarily to reduce soil compaction and improve porosity. In U.S. Pat. No. 5,714,263 (Jakubisin), rubber slivers are encapsulated within a protective resin film, said to be decorative, color-fast and weather-resistant.
Several layered loose-fill constructions are disclosed in U.S. Pat. No. 5,026,207 (Heath), including a top layer of wood fiber, a resilient open mesh beneath the wood fiber, and a fabric layer (felt) beneath the open mesh. In an alternative construction, a fabric layer also is provided above the open mesh, between the mesh and the wood fiber. U.S. Pat. No. 4,679,963 (Heath) and U.S. Pat. No. 5,076,726 (Heath) disclose further layered constructions, e.g. a stone layer wrapped in a fabric layer, beneath a wood fiber layer.
Although each of the foregoing constructions is useful under certain conditions, there remains a need for a play surface foundation that affords good impact attenuation (shock absorbing quality), meets other safety criteria, maintains an attractive appearance, facilitates the use of recycled material, and is suitable for upgrading preexisting playgrounds and other recreational areas, as well as new construction.